Addition/Correction pubs.acs.org/JAFC
Correction to Three Novel Alkaloids from Portulaca oleracea L. and Their Anti-inflammatory Effects Cui-Yu Li,† Yi-Han Meng,† Zhe-Ming Ying,‡ Nan Xu,† Dong Hao,† Ming-Zhe Gao,§ Wen-Jie Zhang,† Liang Xu,† Yu-Cong Gao,† Didier Stien,⊥ and Xi-Xiang Ying*,† †
School of Pharmacy, Liaoning University of Traditional Chinese Medicine, 116600 Dalian, China School of The First Clinic, Liaoning University of Traditional Chinese Medicine, 110032 Shenyang, China § Dalian Institute of Chemical Physics, 116023 Dalian, China ⊥ Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Biodiversité et Biotechnologies Microbiennes (LBBM), Observatoire Océanologique, Banyuls-sur-Mer, France ‡
J. Agric. Food Chem. 2016, 64 (29), 5836−5844. DOI: 10.1021/acs.jafc.6b02673 ABSTRACT: Oleracimine and oleracimine A were isolated from Portulaca oleracea L. and described in the J. Agric. Food Chem, but the alternative structures of the two compounds are proposed on the basis of NMR analyses. KEYWORDS: oleracimine, Portulaca oleracea L., structure elucidation
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INTRODUCTION
DISCUSSION The 1H NMR, 13C NMR, and DEPT spectra of compound 1 showed 18 carbon resonances, including 7 methyls, 2 methylenes, and 9 quaternary carbons including 1 carbonyl, 5 olefinic carbons, and 3 aliphatic carbons. Additionally, one active hydrogen (δH‑6 4.08, 1H, br s) was observed. The 1H NMR (500 MHz, CDCl3) and 13C NMR (125 MHz, CDCl3) data are listed in Table 1. Compound 1 had two gem-dimethyl systems univocally identified on the basis of HMBC correlations of H-10/C-11 and H-11/C-10 and H-14/C-15 and H-15/C-14 couplings. Because all methyl signals were singlet, it was concluded that these two pairs of methyl groups were linked to quaternary carbons. The HMBC (Figure 2) spectrum showed cross-peaks of H1-6/C-4b, C-8, and C-15; Ha-8/C-7, C-8a, C-9, and C-16; Hb-8/C-4b, C-7, C-8a, and C16; Ha-9/C-2, C-8, C-8a, C-9a, and C-16; Hb-9/C-2, C-4a, C4b, C-8a, C-9a, and C-16; H3-13/C-4b and C-5; H3-14/C-7, C8, and C-15; H3-15/C-7, C-8, and C-14; and H3-16/C-4b, C-8, C-8a, and C-9. It can be concluded that two methyls (C-14, C15) were located at C-7 and that methyl C-13 was located at C5. According to the identified methyls and their neighboring carbons, a six-membered ring and a five-membered ring sharing the same two carbon (C-4b and C-8a) atoms were indicated, among which N was connected between C-5 and C-7 because of the downfield 13C NMR chemical shifts (δC‑5 141.0, δC‑7 50.6). The first ring had three aliphatic carbons, two olefinic carbons, and a nitrogen atom; the second ring had two aliphatic carbons and three olefinic carbons. The HMBC showed the cross-peaks of H3-10/C-2, C-3, and C-11; H3-11/C-2, C-3, and C-10; and H3-12/C-3, C-4, and C-4a, suggesting two methyls (C-10, C-11) were located at C-2; methyl C-12 was located at C-4. In a similar way, a second six-membered ring fragment having two identical (C-4a, C-9a) atoms with the five-
In the search for anti-inflammatory agents from Portulaca oleracea L., our group has conducted a well-kept purification work aiming at isolating and characterizing minor constituents of this plant.1 New alkaloids have been isolated, among which are tricyclic metabolites named oleracimine (1) and oleracimine A (2). However, the proposed structures of two compounds (Figure 1) were erroneous, as commented by Dr. Didier Stien, and were therefore revised on the basis of the NMR analyses. Because of Dr. Stien’s significant contribution to correcting our original work, he has been added as an author in the above listing.
Figure 1. Structures of compounds 1 and 2 isolated from Portulaca oleracea: 1, revised structure of oleracimine; 2, revised structure of oleracimine A; 3, published structure of oleracimine; 4, published structure of oleracimine A. © XXXX American Chemical Society
A
DOI: 10.1021/acs.jafc.6b05659 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Journal of Agricultural and Food Chemistry
Addition/Correction
Table 1. 1H NMR (500 MHz) and 13C NMR (125 MHz) Data of Compounds 1 and 2 in CDCl3 1 position
δC, type
1 2 3 4 4a 4b 5 6 7 8
N 65.7, C 206.2, C 121.3, C 143.5, C 110.7, C 141.0, C NH 50.6, C 46.8, CH2
8a 9
38.9, C 52.3, CH2
9a 10 11 12 13 14 15 16
169.4, C 29.1, CH3 27.4, CH3 14.3, CH3 21.1, CH3 28.6, CH3 32.5, CH3 28.8, CH3
2 δH, mult (J in Hz)
δC, type N 65.9, C 206.7, C 122.2, C 140.3, C 110.6, C 142.1, C NH 60.2, C 212.1, C
4.08, br s a: 1.47, d (13.2) b: 2.02, d (13.2)
49.3, C 43.3, CH2
a: 2.28, d (15.3) b: 2.56, d (15.3) 1.31, 1.45, 1.88, 1.82, 1.34, 1.30, 1.17,
166.8, C 28.6, CH3 27.8, CH3 14.7, CH3 22.1, CH3 27.6, CH3 28.4, CH3 25.5, CH3
s s s s s s s
δH, mult (J in Hz)
4.01, br s
a: 2.85, d (17.1) b: 2.61, d (17.1) 1.34, 1.44, 1.95, 2.03, 1.49, 1.37, 1.32,
s s s s s s s
one more carbonyl and one less methylene, including 7 methyls, 1 methylene, and 10 quaternary carbons (2 carbonyls, 5 olefinic carbons, and 3 aliphatic carbons). One active hydrogen (δH‑6 4.01, 1H, br s) was also observed. 1H NMR (500 MHz, CDCl3) and 13C NMR (125 MHz, CDCl3) data are provided in Table 1. Similarly, the HMBC (Figure 2) spectrum of compound 2 showed cross-peaks of H1-6/C-4b; Ha-9/C-8, C-8a, C-9a, and C-16; Hb-9/C-4a, C-4b, C-8a, C-9a, and C-16; H3-10/C-2, C-3, and C-11; H3-11/C-2, C-3, and C-10; H3-12/ C-3, C-4, and C-4a, H3-13/C-4b and C-5; H3-14/C-7, C-8, and C-15; H3-15/C-7, C-8, and C-14; H3-16/C-4b, C-8, C-8a, and C-9, were almost the same as those of compound 1. Hence, it can be assumed these two compounds had the same carbon skeleton. The only difference is methylene replaced by carbonyl at C-8. The relative configuration was confirmed by NOE spectrum, as indicated by correlations of H3-16/Hb-9 and H314; Ha-9/Hb-9, H3-14/H3-15 ,and H3-16, as illustrated in Figure 3. Therefore, the structure of compound 2 was elucidated as 2,2,4,5,7,7,8a-heptamethyl-6,7,8a,9-tetrahydro-2H-cyclopenta[1,2-b:3,4-c′]dipyridine-3,8-dione, named oleracimine A, 2.
Figure 2. Selected 1H−1H COSY and HMBC correlations of compounds 1 and 2.
membered ring aforementioned was figured out. To satisfy the molecular formula, the presence of the nitrogen atom in this ring was reasonable, considering the downfield chemical shift of C-9a (δC 169.4) and C-2 (δC 65.7). The overall structure of compound 1 was further confirmed by additional 2D NMR data (Figure 1). The relative configuration was confirmed by the NOE spectrum, according to the correlations of H3-16/Hb8, Hb-9, and H3-14; Ha-8/Ha-9 and H3-15, H3-12/H3-13, and H1-6/H3-15, as illustrated in Figure 3. Thus, the structure of compound 1 was elucidated as 2,2,4,5,7,7,8a-heptamethyl2,6,7,8,8a,9-hexahydro-3H-cyclopenta[1,2-b:3,4-c′]dipyridin-3one, named oleracimine, 1. The 1H NMR, 13C NMR, and DEPT spectra of compound 2 showed 18 carbon resonances, which was of high similarity with that of compound 1 except for
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AUTHOR INFORMATION
Corresponding Author
*(X.-X.Y.) E-mail:
[email protected]. Phone: +86-041185890139. Fax: +86-0411-85890128. Funding
This work was funded by a project of the National Natural Science Foundation of China (Grant 81573546) and the Natural Science Foundation of Liaoning Province (Grant 2015020699), China.
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REFERENCES
(1) Li, C. Y.; Meng, Y. H.; Ying, Z. M.; Xu, N.; Hao, D.; Gao, M. Z.; Zhang, W. J.; Xu, L.; Gao, Y. C.; Ying, X. X. J. Agric. Food Chem. 2016, 64 (29), 5837−5844.
Figure 3. Selected 1H−1H NOESY correlations of compounds 1 and 2. B
DOI: 10.1021/acs.jafc.6b05659 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
